A variety of engine/transmission mounts and mounting systems for isolating vehicle engine vibration and torsional motion during vehicle operation have been developed. U.S. Pat. No. 2,705,118 to Beck discloses a mounting system including two separate hydraulic mounts each including an elastomer body forming hydraulic damping chambers. These mounts are positioned on the opposite sides of a vehicle engine to support the engine and isolate motion of the engine from the frame. The mounts are in fluid communication with one another through an external piping and adjustable orifice valve arrangement. It is the restricted flow of fluid through the piping which provides the desired degree of vibration and torsional damping. The hydraulic mounts themselves produce only minimal damping effect without this external fluid connection. Because of the remote nature of the mounts requiring relative long connecting piping, proper tuning of the system requires careful adjustment of the valves. This also complicates the installation, and increases the cost of the system. Because the piping is external, it is also prone to damage through accident, improper maintenance or the like.
U.S. Pat. No. 4,572,321 to Morita discloses a hydraulic mounting system including two hydraulic mounts having upper and lower fluid filled chambers. The mounts are oppositely positioned on the engine, and here again are intended to isolate the engine vibration and rocking motions from the vehicle frame. This system also requires external piping and an external control valve requiring at least one pressure signal input from the vehicle suspension system to control the engine rocking.
U.S. Pat. No. 4,610,421 to Ohta et al. discloses a mounting system for an engine/transmission assembly including four mounts. Two spaced mounts are provided on the pitching axis of the engine, but are not connected. These mounts include upper and lower fluid filled chambers. The flow of fluid between the chambers within each mount may be made variable by a solenoid means to provide variable damping. Operation of these mounts requires vehicle suspension and engine motion inputs through a control system, necessarily increasing system complexity and expense.
A need exists therefore for an improved hydraulic mount system to dampen vibration and, in particular, the torsional pitching or rocking motion of vehicle engine/transmission assemblies. The mount assembly of the system would be self contained, require no external controller and be relatively economical to implement.